In genetics, a mutation is a change of the DNA sequence of the genome of an organism. Mutations result from unrepaired damage to DNA or to RNA genomes, from errors in the process of replication (duplication of the DNA), or from the insertion or deletion of segments of DNA.

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Mutations may or may not produce discernible changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes, including evolution, cancer, and the development of the immune system.